A shock absorber has a tubular cylinder, a piston serving as a valve disk inserted into the cylinder so as to move along an axial direction, a rod connected to the piston and provided with one end extending outward of the cylinder, two chambers partitioned by the piston and filled with a hydraulic fluid, a passage that allows these chambers to communicate with each other, and a valve body configured to open and close the passage. In this shock absorber during a telescopic motion, the valve body resists against a flow of the hydraulic fluid passing between the chambers through the passage in order to generate a damping force caused by a pressure difference between the two chambers.
For example, in a piston disclosed in JP2010-196798A, a plurality of expansion-side and contraction-side passages (hereinafter, referred to as an expansion-side passage and a contraction-side passage) penetrating the piston are arranged alternately side by side along a circumferential direction. In this piston, fan-shaped seats that individually surround an outlet port of the expansion-side passage are formed in one side of the piston as many as the number of the expansion-side passages. In the other side of the piston, fan-shaped seats that individually surround an outlet port of the contraction-side passage are formed as many as the number of the contraction-side passages. Furthermore, the piston is provided with a plurality of annular disk-shaped leaf valves. A valve body seated on and unseated from each seat opens and closes the expansion-side passage or the contraction-side passage.
In another piston disclosed in JP2011-149447A, expansion-side and contraction-side passages penetrating the piston are arranged alternately side by side along a circumferential direction. In this piston, an annular seat that integrally surrounds the outlet ports of overall expansion-side passages is formed on one side of the piston, and an annular seat that integrally surrounds the outlet ports of overall contraction-side passages is formed on the other side of the piston. In addition, the piston has a plurality of annular disk-shaped leaf valves so that a valve body seated on and unseated from each seat opens and closes the expansion-side passage or the contraction-side passage.